The present invention provides a coating for glass substrates and the like which resist accumulation of dirt and water stains. Coated glass substrates of the invention can be used in insulated glass units wherein the coating of the invention is carried on an exterior surface of one pane of glass while a reflective coating is applied on the opposite side of the same pane of glass.
Keeping windows and other glass surfaces clean is a relatively expensive, time-consuming process. While cleaning any individual window is not terribly troublesome, keeping a larger number of windows clean can be a significant burden. For example, with modern glass office towers, it takes significant time and expense to have window washers regularly clean the exterior surfaces of the windows.
Windows and other glass surfaces can become xe2x80x9cdirtyxe2x80x9d or xe2x80x9csoiledxe2x80x9d in a variety of ways. Two of the primary manners in which windows can collect dirt involve the action of water on the glass surface. First, the water itself can deposit or collect dirt, minerals or the like onto the surface of the glass. Obviously, dirty water landing on the glass will leave the entrained or dissolved dirt on the glass upon drying. Even if relatively clean water lands on the exterior surface of a window, each water droplet sitting on the window will tend to collect dust and other airborne particles as it dries. These particles and any other chemicals which become dissolved in the water will become more concentrated over time, leaving a characteristic spot or drying ring on the glass surface.
The second way in which water tends to give a window or other glass surface a soiled or less attractive appearance is tied to an attack on the glass surface itself. As a droplet of even relatively clean water sits on a glass surface, it will begin to leach alkaline components from the glass. For a typical soda lime glass, the soda and lime will be leached out of the glass, increasing the pH of the droplet. As the pH increases, the attack on the glass surface will become more aggressive. As a result, the glass which underlies a drying water droplet will become a little bit rougher by the time the water droplet completely dries. In addition, the alkaline components which were leached out of the glass will be redeposited on the glass surface as a drying ring. This dried alkaline material not only detracts from the appearance of the glass; it will also tend to go back into solution when the glass surface is wetted again, rapidly increasing the pH of the next water droplet to coalesce on the glass surface.
In storing and shipping plate glass, the presence of water on the surfaces between adjacent glass sheets is a chronic problem. One can take steps to shield the glass from direct contact with water. However, if the glass is stored in a humid environment, water can condense on the glass surface from the atmosphere.
This becomes more problematic when larger stacks of glass are collected. Large stacks of glass have a fairly large thermal mass and will take a long time to warm up. As a consequence, they will often be cooler than the ambient air when ambient temperature increases (e.g., in the morning), causing moisture in the air to condense on the surface of the glass. Due to limited air circulation, any moisture which does condense between the sheets of glass will take quite a while to dry. This gives the condensed moisture a chance to leach the alkaline components out of the glass and adversely affect the glass surface. The rate of attack can be slowed down somewhat by applying an acid to the surface of the glass. This is commonly done by including a mild acid, e.g., adipic acid, in the separating agent used to keep glass sheets from sticking to and scratching one another.
A number of attempts have been made to enable a glass sheet to keep a clean appearance longer. One avenue of current investigation is a xe2x80x9cself-cleaningxe2x80x9d surface for glass and other ceramics. Research in this area is founded on the ability of certain metal oxides to absorb ultraviolet light and photocatalytically break down biological materials such as oil, plant matter, fats and greases, etc. The most powerful of these photocatalytic metal oxides appears to be titanium dioxide, though other metal oxides which appear to have this photocatalytic effect include oxides of iron, silver, copper, tungsten, aluminum, zinc, strontium, palladium, gold, platinum, nickel and cobalt.
While such photocatalytic coatings may have some benefit in removing materials of biological origin, their direct impact on other materials is unclear and appears to vary with exposure to ultraviolet light. As a consequence, the above-noted problems associated with water on the surface of such coated glasses would not be directly addressed by such photocatalytic coatings.
A number of attempts have been made to minimize the effect of water on glass surfaces by causing the water to bead into small droplets. For example, U.S. Pat. No. 5,424,130 (Nakanishi, et al., the teachings of which are incorporated herein by reference) suggests coating a glass surface with a silica-based coating which incorporates fluoroalkyl groups. The reference teaches applying a silicone alkoxide paint onto the surface of the glass, drying the paint and then burning the dried paint in air. Nakanishi, et al. stress the importance of substituting part of the non-metalic atoms, i.e., oxygen in a layer of SiO2, with a fluoroalkyl group. Up to 1.5% of the oxygen atoms should be so substituted. Nakanishi, et al. state that if less than 0.1% of the oxygen atoms are substituted with a fluoroalkyl group, the glass won""t repel water properly because the contact angle of water on the glass surface will be less than 80xc2x0.
Such xe2x80x9cwater repellentxe2x80x9d coatings do tend to cause water on the surface of the glass to bead up. If the coating is applied to an automobile windshield or the like where a constant flow of high velocity air is blowing over the surface, this water beading effect can help remove water from the glass surface by allowing the droplets to blow off the surface. However, in more quiescent applications, these droplets will tend to sit on the surface of the glass and slowly evaporate. As a consequence, this supposed xe2x80x9cwater repellentxe2x80x9d coating will not solve the water-related staining problems noted above. To the contrary, by causing the water to bead up more readily, it may actually exacerbate the problem.
Other silica coatings have been applied to the surface of glass in various fashions. For example, U.S. Pat. No. 5,394,269 (Takamatsu, et al.) proposes a xe2x80x9cminutely roughxe2x80x9d silica layer on the surface of glass to reduce reflection. This roughened surface is achieved by treating the surface with a supersaturated silica solution in hydrosilicofluoric acid to apply a porous layer of silica on the glass sheet. By using a multi-component of sol gel solution, they claim to achieve a surface which has small pits interspersed with small xe2x80x9cislet-like land regionsxe2x80x9d which are said to range from about 50-200 nm in size. While this roughened surface may help reduce reflection at the air/glass interface, it appears unlikely to reduce the water-related staining problems discussed above. If anything, the porous nature of this coating appears more likely to retain water on the surface of the glass. In so doing, it seems probable that the problems associated with the long-term residence of water on the glass surface would be increased.
In one aspect, the present invention provides a glass article which has a water-sheeting coating and a method of applying such a coating. In accordance with a first embodiment of this invention, a glass article has at least one coated surface bearing a water-sheeting coating. This water-sheeting coating comprises silica sputtered directly onto an exterior surface of the glass. The water-sheeting coating has an exterior face which is substantially non-porous, but which has an irregular surface. This water-sheeting coating desirably reduces the wetting angle of water on the coated surface of the glass article below about 25xc2x0 and causes water applied to the coated surface of the glass article to sheet.
In accordance with a second embodiment of the invention, a window is provided having at least one pane of glass having an exterior surface exposed to periodic contact with water. The exterior surface of this pane of glass has a water-sheeting coating comprising silica sputtered directly on the glass surface to a mean thickness of between about 15 xc3x85 and about 350 xc3x85. This water-sheeting coating has an exterior face which is substantially non-porous, but which has an irregular surface. The water-sheeting coating causes water applied to the coated surface of the pane of glass to sheet.
In a further embodiment of the invention, a sheet of glass has an interior surface bearing a reflective coating thereon and an exterior surface bearing a water-sheeting coating thereon. The reflective coating may comprise a reflective metal layer and at least one dielectric layer. The water-sheeting coating again comprises silica sputtered directly onto the exterior surface of the sheet of glass and this water-sheeting coating has an exterior face which is substantially non-porous, but which has an irregular surface. This water-sheeting coating desirably reduces the contact angle of water on the coated surface of the sheet of glass below about 25xc2x0 and causes water applied to the coated exterior surface of the pane to sheet.
As noted above, the present invention also contemplates a method of rendering a glass surface resistant to soiling and staining. In one embodiment, the method comprises first providing a sheet of glass having an interior surface and an exterior surface. The interior and exterior surfaces of the glass are cleaned. Thereafter, the interior surface of the sheet of glass is coated with a reflective coating by sputtering, in sequence, at least one first dielectric layer, at least one metal layer, and at least one second dielectric layer. The exterior surface of the glass is coated with a water-sheeting coating by sputtering silica directly onto the exterior surface of the sheet of glass. If so desired, the water-sheeting coating can be applied on the same sputter coating apparatus used to create the reflective coating. With appropriate material selection, the water-sheeting coating and one of the dielectric layers of the reflective coating may even be applied in the same sputtering chamber in an oxidizing atmosphere. If so desired, the pane of glass can be coated on both the interior surface and the exterior surface while maintaining the glass in a constant orientation wherein the interior surface is positioned above the exterior surface.
In accordance with an alternative method of the invention, a sheet of glass having an interior surface and an exterior surface is provided. A sputtering line is also provided, the sputtering line comprising a series of sputtering chambers, each having a support for a sheet of glass therein. At least one of the sputtering chambers comprises a dual direction sputtering chamber having an upper target position above the support and a lower target position below the support. The interior and exterior surface of the glass are cleaned and, thereafter, the sheet of glass is positioned on the support in the dual direction supporting chamber such that the interior surface is oriented toward the upper target and the exterior surface is oriented toward the lower target. The upper target is sputtered to deposit a dielectric layer. This dielectric layer may be deposited directly on the interior surface of the glass or on a film stack layer previously deposited on the interior surface of the glass. While the sheet of glass remains in the dual direction sputtering chamber, the lower target is sputtered to deposit a water-sheeting coating on the exterior surface of the glass. In one possible preferred embodiment, both the upper target and the lower target are sputtered in an oxidizing atmosphere within the same sputtering chamber.
In yet another embodiment, the invention provides a method of coating two sides of a single pane of glass or other substrate in a single pass through a coating apparatus, regardless of the nature of the coating being applied to either side of the glass. In this method, a sheet of glass (or other substrate) having a clean interior surface and a clean exterior surface is provided. A sputtering line is also provided, this line comprising a series of sputtering chambers each having a support for a sheet of glass therein, at least one of the sputtering chambers comprising a downward sputtering chamber having an upper target positioned above the support. A second of the sputtering chambers comprises an upward sputtering chamber having a lower target positioned below the support. The sheet of glass or other substrate is positioned on the support in the downward sputtering chamber such that the interior surface is oriented toward the upper target. The upper target is sputtered to deposit a coating directly on one of the interior surface of the glass or a film stack layer previously deposited on the interior surface of the glass. The sheet of glass is also positioned on the support in the upward sputtering chamber such that the exterior surface is oriented toward the lower target. The lower target is sputtered to deposit a coating on one of the exterior surface of the glass or a film stack layer previously deposited on the exterior surface of the glass. The glass is coated on both the interior surface and the exterior surface while maintaining a constant orientation wherein the interior surface is positioned above the exterior surface.
In still another embodiment, there is provided a glass article with an interior surface and an exterior surface. The interior surface bears a first water-sheeting coating and the exterior surface bears a second water-sheeting coating. The first and second water-sheeting coatings each comprise silica sputtered directly onto the respective surface of the glass article and each has an exterior face that is substantially non-porous but has an irregular surface. The first and second water-sheeting coatings each reduce the contact angle of water on the respective surfaces below 25xc2x0 and cause water applied thereto to sheet.
In another embodiment, a multi-pane insulated glass unit is provided. The unit includes first and second panes of glass held in a spaced-apart relationship by a spacer to define a sealed interpane space. The first pane has an exterior surface oriented away from the second pane. This exterior surface is also exposed to periodic contact with water. The second pane has an interior surface exposed to the interpane space and an exterior surface oriented away from the first pane. A first water-sheeting coating is carried on the exterior surface of the first pane. A second water-sheeting coating is carried on the exterior surface of the second pane. The first and second water-sheeting coatings each comprising silica sputtered directly onto the respective surface of the first and second panes. The first and second water-sheeting coatings each have an exterior face that is substantially non-porous but has an irregular surface. The first and second water-sheeting coatings each reduce the contact angle of water on the respective surface of the first and second panes to below 25xc2x0 and cause water applied thereto to sheet.
In yet another embodiment, there is provided a method of rendering surfaces of a pane of glass resistant to soiling and staining. A sheet of glass having a clean interior surface and a clean exterior surface is provided. Silica is sputtered directly onto the interior surface of the sheet of glass to yield a first water-sheeting coating having a contact angle with water below about 25xc2x0 which causes water applied to said interior surface to sheet. Silica is also sputtered directly onto the exterior surface of the sheet of glass to yield a second water-sheeting coating having a contact angle with water below about 25xc2x0 which causes water applied to said exterior surface to sheet.
In still another embodiment, a method of coating two sides of a pane of glass in a single pass through a coating apparatus is provided. A sheet of glass having a clean first surface and a clean second surface is provided. A sputtering chamber having a plurality of rollers that define a substrate support therein is provided. The chamber has an upper target positioned above the support that is adapted to downwardly sputter. The chamber also has a lower target positioned below the support that is adapted to upwardly sputter. The sheet of glass is positioned in the chamber such that the first surface of the sheet of glass rests on one or more of the rollers and is oriented toward the lower target. With the sheet of glass in this position, the second surface of the sheet of glass is oriented toward the upper target. The lower target is sputtered to deposit a first water-sheeting coating on the first surface of the glass. The first water-sheeting coating has a contact angle with water below about 25xc2x0 which causes water applied to said first surface to sheet. The upper target is sputtered to deposit a second water-sheeting coating on the second surface of the glass. The second water-sheeting coating has a contact angle with water below about 25xc2x0 which causes water applied to said second surface to sheet.
In another embodiment, there is provided a method of rendering a glass surface resistant to soiling and staining. A sheet of glass having a clean interior surface and a clean exterior surface is provided. A sputtering line comprising a series of sputtering chambers is provided. Each sputtering chamber in the line has a plurality of rollers that define a substrate support. The sputtering line includes an upward sputtering chamber with a lower target positioned below the rollers in that chamber. The sheet of glass of is positioned in the upward sputtering chamber such that the exterior surface of the sheet of glass rests on two or more of the rollers in that chamber. The lower target is sputtered to deposit silica directly onto the exterior surface of the glass to yield a water-sheeting coating having a contact angle with water below about 25xc2x0 which causes water applied to the exterior surface to sheet. The sputtered silica travels between said two or more rollers before being deposited on the exterior surface of the sheet of glass.